This invention pertains to a windshield wiper installation, especially for motor vehicles.
When vehicle speed is high the air impinging upon the windshield streams away from the windshield upwards and to both sides under such a high pressure that it creates an ascending force at the wiper blades and wiper arms. Thus, the contact between the windshield and the wiper blade is diminished so that the cleaning effect of the windshield wiper installation is reduced. The problem is especially pronounced in considerably curved lateral areas of the windshield. For the safety of all road users, it is however, necessary that the windshield is cleaned properly also at high speeds.
To reduce the tendency of the wiper blades to lift from the windscreen or avoid it completely, various designs of windshield wiper installations are known. In some of these installations spoilers or other aerodynamic surfaces are attached on the wiper blades and/or wiper arms to produce an additional pressure which is effective against the ascending force. In contrast thereto another windshield wiper installation, described in German specification OS No. 2,824,014, is designed in such a way that by manipulations of the wiper arm spring various contact pressure values can be provided even while the vehicle is moving and when the wipers are operating. Such a windshield wiper installation is not only suitable for providing a higher contact pressure at high vehicle speeds than at lower vehicle speeds, but also for reducing the contact pressure when the wipers are not operating and the wiper blades occupy the parking position. By this measure the pressure is removed from the wiper rubber, so that wear is reduced.
In the windshield wiper installation of German specification OS No. 2,824,014 the main parts of the wiper arm are a wiper arm head, a swivelling member and a wiper arm spring which is suspended on the first mentioned parts. The swiveling member is normally composed of a link and a wiper rod. The wiper arm head includes a fastening member which is mounted on the wiper shaft in a manner protected against twisting and a holding member on which the wiper arm spring acts. The holding member is developed as a two-armed lever which is tiltably mounted on the fastening member and which can be displaced relative to the fastening member of the wiper arm head by means of a rod which extends in the hollow wiper shaft. An imagiary line may be drawn between the suspension point of the wiper arm spring on the swiveling member and on the holding member. The distance of this imaginary line from the articulated axle between the fastening member and the swiveling member is changed by such a displacement so that the lever arm producing the contact pressure and thus, the contact pressure itself becomes greater or smaller. One disadvantage of that windshield wiper installation is than an additional rod is necessary for changing the relative position between the fastening member and the holding member of the wiper arm head and further that the wiper shaft has to be hollow.